The invention relates to a decision circuit that is more particularly described as a reshaping and retiming circuit which reshapes input pulses into squared-up output pulses even upon failure of timing signals.
In the prior art, a regenerator in a digital transmission system extracts timing or clock signals from a received data stream. The extracted timing signals are used for controlling the regeneration, that is, the reshaping and retiming of data bits being received. If the timing extraction arrangement fails for any reason, a problem arises in that the regenerator ceases to regenerate the received data bits. No output signals are transmitted further along the line.
In the prior art, a regenerator makes a binary decision concerning the amplitude of a received digital signal with respect to a predetermined threshold level at an optimum sampling instant. In response to the received data signal and an extracted timing signal, a prior art decision circuit in the regenerator reshapes and retimes the received signal into a regenerated, or reshaped and retimed, output signal. This regenerated output signal, with as little distortion as possible, is applied to a modulator for shaping an output signal to be transmitted further along the transmission line.
The prior art decision circuit functions in response to a timing signal that is extracted from the received stream of data bits. A problem occurs if the timing extraction circuit fails to extract the timing signal from the received stream of data bits. The problem is that without application of the timing signal the prior art decision circuit ceases to reproduce and retransmit the received data signals.